Rising energy costs and the intensification of legal regulations with regard to the permissible fuel consumption or the permissible emission of noxious substances by motor vehicles in which internal combustion engines have been fitted make it necessary to take measures to reduce the fuel consumption of internal combustion engines, on the one hand, and, on the other hand, to ensure that the emission of noxious substances by the motor vehicle is kept at a low level. In this context, it has become a well known fact that internal combustion engines, in particular gasoline-operated internal combustion engines, must be operated at specific operating points with a self-igniting combustion method, which is also referred to as Homogeneous Charge Compression (HCCI) Ignition, Compressed Auto Ignition (CAI), or a space ignition method (RZV). In the case of such a self-igniting combustion method, the self-ignition and thereby the combustion curve are controlled via the reactive quantity of energy in the cylinder of the internal combustion engine. This quantity of energy is provided amongst others by a very large volume of residual gas compared with the conventionally ignited spark ignition engine operation or gasoline engine operation. Even for conventionally ignited spark ignition engines or gasoline engines it is a well known fact that the internal combustion engine must be operated at the lower and the medium partial load range with a high exhaust gas return rate in order to optimize the combustion with regard to the quality criteria referred to as the fuel consumption and the emission of noxious substances.
A method for determining a combustion chamber pressure curve in the case of an internal combustion engine is known from DE 199 007 38 C1. In this method, an estimated value of a cylinder pressure is estimated from a previous measured value of the cylinder pressure, a volume of the cylinder allocated to this and a volume of the cylinder allocated to the estimated value of the cylinder pressure and a polytropic exponent by means of the polytropic equation. The polytropic exponent is predetermined as a function of a coolant temperature.
An additional method for determining the pressure of a combustion chamber in a cylinder of an internal combustion engine is known from EP 0 399 069 A1. This involves determining a sensitivity of the cylinder pressure sensor allocated to said internal combustion engine in each working cycle of the cylinder and doing this as a function of three voltage measuring signals and a predetermined polytropic exponent.